It doesn't have to be ray-traced, or dynamically shadow-mapped, it can be approximated with just a projection of the cloud texture onto the surface texture as a subtractive layer, or something. That's probably how Celestia did it, right

It sounds easy, but in reality it is not easy. Each planet in SE have a lot of textures (200-300 at ground level), mapped on a square-shaped tiles of landscape. Clouds layers uses the same technique. So it is impossible to make "just a projection" - each cloud tile may project on many landscape tiles, and each landscape tile may recieve shadow from many cloud tiles. So easiest way is to implement usual shadow mapping.

Or would it be too tempting to 'kill two birds with one stone', and implement landscape shadowing - and possibly drive up the computational load too much?

EDIT

Quote (HarbingerDawn)

It threw me off because he asked about ring shadows, not cloud shadows, but then changed direction and described cloud shadows and not ring shadows. So I just answered the question that he asked most clearly.

Yes, my wording was a little ambiguous, sorry about that. I was actually asking if the technique used currently to cast ring shadows would work with the different cloud-belt textures.

Thinking about it further (and with a clearer head), I imagine that the ring shadows are not mapped at all, but rather take their cue from the density variations in the ring algorithm's output for the planet in question - drawing bands of darkness along the appropriate path on cloud, atmosphere, and landscape models.

Or would it be too tempting to 'kill two birds with one stone', and implement landscape shadowing - and possibly drive up the computational load too much?

Its been mentioned that whatever exists in real astronomy will be implemented so I assume that stuff would be added eventually. I doubt it would be too heavy on resources if 64 bit support is eventually added, plenty of modern games do far more things at once.

When we name our own star's we'll be able to have them labeled too, right?

You could find a remote planet a few megaparsecs away and imagine your own civilization there; you could pick stars out from that planet's pov and name them as if you were an inhabitant looking up at the stars.

You could find a remote planet a few megaparsecs away and imagine your own civilization there; you could pick stars out from that planet's pov and name them as if you were an inhabitant looking up at the stars.